Selector system



Jan. 7, 1930. F. A.'KOLSTER SELECTOR SYSTEM Filed Nov. 22, 1926 IF 'IE 'L nv nu r'on fi'eder/ck A. Ko/sfer fi/j ATTaRHEYs Patented Jan. 7, 1930 UNITED STATES PATENT OFFICE FREDERICK A. KOLSTER, OF PALO ALTO, CALIFORNIA, ASSIGNOR TO FEDERAL TELE- GRAPH COMPANY, OF SAN FRANCISCO,

FOBNIA CALIFORNIA, A CORPORATION OF CALI- SELECTOR SYSTEM Application filed November 22, 1926. Serial No.'149,814.

This invention relates generally to selective audio frequency wave translating systems and particularly audio amplifiers in radio circuits for receiving radio-compass signals.

An object of the invention is to improve the selectivity of audio amplifying systems.

Referring to the drawings:

Figure 1 is a circuit diagram illustrating the principles of this invention as applied to the receiving apparatus of a radio compass.

Fig. 2 is a circuit diagram illustrating the principles of this invention as applied to general radio apparatus.

The system of this invention is characterized by the use of two coils which are associated with one circuit and which coils are electrically coupled to a second circuit for transferring electrical energy. Energy is admitted to one coil regardless of frequency while energy is admitted to the other coil to neutralize the efiect of the first coil for all frequencies lying outside the desired freuency band. Therefore while energy will ow in the first circuit regardless of frequency, energy will be'transferred to'the secgnd circuit on y within the desired frequency and.

The radio system shown in Fig. 1 with which the invention has been incorporated, comprises a suitable antenna for the absorp tion of radio energy. As the specific system illustrated is to be used for the purpose of a radio compass I have illustrated a directive antenna such as a rotary loop 10 tuned by suitable means such as a capacitance 11. The energy received from the antenna is preferably amplified one or more times by suitable means such as a radio frequency amplifier indicated diagrammatically at 12. The amplified energy from the amplifier 12 is then impressed upon a suitable detector or indicating device indicated generally at 13, which in th1s instance is an electron emission tube comprising a grid or control electrode 14, filament or electron emission element 15, and the plate .or anode 16. The output circuit of detector'13 which has been indicated generally at 17 is electrically coupled with the input circuit 18 of an electron emission amplifier indicated generally at 19. The electron emission amplifier tube 19 is of the usual three element type comprising a grid 20, electron emission element 21 and plate or anode 22. The output circuit of-this tube, designated generally at 23, may be further coupled to further amplifiers or to a'work circuit designated at 24 which supplies energy to a translator indicated at 25.

Generally in coupling together the stages of an audio frequency amplifier, iron core transformers of relatively high impedance are utilized. these transformer having a primary winding supplied from he output of a tube or detector and having a secondary winding supplying the input of a succeeding an'ipliiier tube. Such an arrangement will transmit substantially all electrical energy within the range of audibility. Thus if the radio system described above were to be constructed with ordinary coupling transformers and used for the reception of a signal having a definite tone or having a definite signal frequency Within audibility, as in receiving radio compass bearing signals, the audio frequency amplifier would not only amplify the energy representing the signal but would also amplify stray impulses of different frequencies as well as impulses caused by static 'distnrbances or by tube noises. ince radio compasses are generally used-on ships, stray impulses are especially prevalent as they originate from the commutators of the ships dynamos and from the general electrical equipment. In this invention the coupling device is designed to transmit efliciently only a narrow band of audio frequencies and thereby eliminate in- "'trfering frequencies lying outside this narthe translator 25. It is obioo hood of say 500 cycles.

quency the filter transformer which, in case the device is to be used for energy at audio frequency, is provided with a magnetic core 29 upon which 1s wound a air of primary coils 30 and 31 and a secon ary coil 32. The primary coils may be formed as asingle continuous winding provided withan intermediate or central tap 33. One of the primary coils, say the coil 31, is connected directly across the output circuit 17 of detector tube 13 in series with a filter device designated generally at 36. This filter device preferably comprises an inductance 37 shunted by a capacitance 38 and is tuned so as to form a circuit resonant for the narrow band of frequencies which it is desired to transfer to the circuit 18. In practice the coils 30 and 31 are wound so as not to be resonant for any frequency for which the system will be called upon to transmit.

In explainin the operation of the above system it will epresumed that the system is designed and adapted to receive energy having a signal frequency in the neighbor- In addition to energy at this signal frequency the detector 13 will also receive interfering energy at frequencies differing substantiall from this signal frequency, as for examp e stray impulses, static, etc. All of this energy received will be impressed upon the output circuit 17 of the detector and also upon the coil 30 since this coil is not resonant to any one frequency within audibility. A portion of the current in the output circuit 17 will also flow through primary coil 31 and the filter device 36 since for fre uencies lying outside the desired freand the filter device 36 will be nonresonant and will therefore offer a path of low impedance. The coils 30 and 31 are wound so that this current flowing in coil 31 will set up a field which will tend to neutralize the field of coil 30, so that a minimum of energy will be transferred to the input circuit 18 for frequencies 1 ing'outside the desired frequency band. owever,'for the desired signal frequenc or for frequencies lying within the desire frequency band, device 36 will be resonant so as to offer a path of high impedance for currents of this frequency in the output circuit 17. Accordingly, the field of coil 31 will not tend to neutralize the field of coil 30 and energy of the desired signal frequency will be transmitted to the input circuit 18. With this form of coupling arrangement it has been found that interfering noises in the translator 25 may be greatly suppressed without substantially diminishing the intensity of the desired signal tone.

In Fig. 2 I have illustrated the invention as being utilized for the purposeof selectivel transferring energy at radio frequency f iom one circuit to another. One circuit in this instance is represented by the antenna40 and ground 41 with which are associated the coils 42 and 43. These coils may be formed of one continuous winding, to the center tap of which is connected the antenna 40. The outer terminal of one coil, say the coil 42, is connected directly to ground 41, while the outer terminal of the other coil 43 is connected to the ground in series with a filter device 45. This filter device is similar to the filter 36 described above and comprises an inductance 46 shunted by variable capacitance 47. Coils 42 and 43 are proportioned so as to be non-resonant for any radio frequency within the range for which the system is adapted to be operated, as by having a natural wave length period which is longer than the longest wave length which it is desired to receive. The coils 42 and 43 are both electrically coupled to another circuit 48 as by means of a secondary coil 49. In the particular radio receiver shown the second circuit 45 forms the input circuit of electron emission amplifier 50. this amplifier having its output circuit 51 coupled to further amplifiers or a detector and translator indicated generally at 52. Another coupling device 53 similar to the device for coupling the antenna to the amplifier tube 50 may be employed for coupling the output circuit 51 with the detector or amplifier 52.

In operating the above arrangement the variable ca'pacitance47 is adjusted until the filter device 45 is reasonant to the frequency of the desired radio frequency signals. For energy differing in frequency from the desired signals the filter device 45 will present a path of low impedance with the result that this energy will divide itself between coils 42 and 43 in such a way that the fields of these coils will neutralize each other. However, for signals of the desired frequency the filter device 45 will impose a high impedance in series with coil 43 with the result that no energy will'be admitted to coil 43 to neutralize the energy admitted to coil 42. Thus coil 42 will effect a transfer of energy at the selected frequency to thecircuit 48 and thus to the amplifier 50.1 At the same time the resonant condition of the filter 45 will set up a circulatory current through coils 42 and 43 in series to act cumulatively or additively with the coil 42, thus increasing the efficiency of energy transfer. The coupling unit 53 between the output 51 and the amplifier or detector 52 is similar to the coupling device for transferring energy from the antenna circuit to the input circuit 48 and is likewise selectively controlled by adjustment of a variable capisitance 47 I claim:

1. In an audio frequency translating system, a source of audio frequency waves, a transformer having-a magnetic core, two primary windings and a secondary winding,

v with audio waves of a narrow range of freguencies, an antenna, amplifying and detect- 1 ng means associated therewith, and a selective audio frequency translatinfg system comprislng a magnetic core trans ormer havin a secondary winding and two prima win ings, the latter being differentially connected to the output of said detector circuit, a load circuit connected to the secondary wmd' and an inductanceand condenser 1n paralllfi combination, said combination connected in series with one of said primary windings and being tuned to the desired audio frequency. In testimony whereof, I have hereunto set my hand.

FREDERICK A. KOLSTER 

